I really want HA starters the most, they've had multiple chances to make them events, such as the movie or the TCG boxes, so I'm really hoping they were just saving them for USUM. I really need Intimidate Incineroar in my life, please game freak let us use the Alola starters at their full potential before we leave Alola.
Actually, Long Reach won't really do much on Decidueye aside from simply circumvent Garchomp's and Ferrothorn's abilities, which both can overwhelm it. Liquid Voice, on the other hand, will most likely make a splash (pun intended) in VGC or simply DOU, because its main Normal-type spread move will end up getting boosted by STAB, so it'll essentially just be a Water-type version of Aerilate, but with sound-based moves and without the 20% boost. Even in UU as well Primarina will end up being a threat, and while it outclasses Sylveon right now, that will probably put the kibosh on its time in UU, and it'll probably rise to OU as a result, where it'll end up threatening the likes of Garchomp and Lando-T.
I doubt Primarina's HA is going to do too much for her, the only move she has that takes advantage of it is Hyper Voice, a 90 Base power spread sound move, and she already gets a water type move that's nearly identical in Sparkling Aria, only difference is it doesn't hit the Ally.
Making one specific move not hit an Ally is not much of a mayor improvement, it's nice to have regardless, but I feel like the other two need their abilities a lot more. (Primarina is pretty good on her own regardless)
Decidueye gets to avoid damage from Rocky helemt, Rough Skin and iron barbs, aswell as doing regular damage to fur coat and fluffy user, and also avoids getting statuses from flame body, static, poison touch, tangling hair and all those Haxy abilities. Situational, but pretty useful regardless, I've lost a couple of battles because of badly timed static paralisis or flame body's effects.
Incineroar's Intimidate is going to be awesome because his movepool is perfect for it (Mostly VGC/doubles), he gets both Fake Out and U-turn, both extremelly useful moves for Intimidate users (And as far as I know, he is the only one to get both of them), aswell as some other annoying support moves like Snarl.
As of now he doesn't really stand out, but when he gets his HA he is gonna be grrrrreat!